A power conversion device which includes two serially-connected SW elements of an upper arm and a lower arm and supplies power to a load by converting a voltage and a current from a DC power supply is disclosed, for example, in JP2005-287267A (Patent Literature 1).
A power conversion device employed in a vehicle is required to have high power density (compact size and large current) and a small power loss. To this end, a current, a voltage, and a switching speed (hereinafter, referred to as a SW speed) of the SW elements are kept increased. When a current, a voltage, and a SW speed of the SW elements which supplies power are increased, however, a surge voltage occurring at the time of switching is increased. In order to reduce a switching loss (hereinafter, referred to as a SW loss), it is absolutely necessary to restrict the surge voltage. The surge voltage also depends on a value of floating inductance in an interior of a filter capacitor or a power module forming the power conversion device or in a bus bar electrically connecting the foregoing components, and the surge voltage becomes high when the floating inductance is large.
The power conversion device disclosed in Patent Literature 1 includes power modules in each of which the SW element is molded with resin in the shape of a flat rectangular parallelepiped. A positive electrode and a negative electrode are provided on one flat surface of the power module and the other surface forming a heat-sinking plane is connected to a cooling substrate. A positive (upper arm) power module group and a negative (lower arm) power module group are disposed in such a manner that the respective surfaces provided with the electrodes oppose each other at a predetermined interval and form a two-way path in which currents flowing in and out from the respective modules oppose each other. Owing to the location and the configuration of the power modules as above, the power conversion device of Patent Literature 1 restricts a surge voltage to be low by reducing the floating inductance occurring between the power modules.
On the other hand, when a larger current flows, the SW elements generate a larger amount of heat while in use. It thus also becomes necessary to enhance radiation performance of the SW elements. A SW element with excellent radiation performance is disclosed, for example, in JP2003-110064A (Patent Literature 2).
The SW element disclosed in Patent Literature 2 is a double-sided heat-sinking element module. The element module has a structure in which a pair of heat sinks is bonded to both surfaces of a semiconductor chip, for example, via solder layers, and the element module is entirely molded with resin in such a manner that respective outer surfaces of a pair of the heat sinks are exposed. Accordingly, heat can be released from the both surfaces of the semiconductor chip and high radiation performance can be exerted. The element module of Patent Literature 2 is also shaped like a flat rectangular parallelepiped. However, different from the power module in Patent Literature 1, the heat sink exposed to one flat surface forms a positive electrode and the heat sink exposed to the other surface forms a negative electrode.